Two months before his death, Shoghi Effendi sent a cablegram announcing "Purification of Haram-i-Aqdas."

On September 6, 1957, two months before his death, Shoghi Effendi sent a cablegram announcing "Purification of Haram-i-Aqdas." This purification would be completed by the Universal House of Justice with the removal of the remains of Bahá'u'lláh's son Mirza Díyá'u'lláh, which had laid beside his father.

Purification of Haram-i-Aqdas
Announce to Hands and all National Assemblies that following the loss of the appeal to the Supreme Court, the Government expropriation order has been implemented, resulting in the complete evacuation of the remnant of Covenant-breakers and the transfer of all their belongings from the precincts of the Most Holy Shrine, and the purification, after six long decades, of the Haram-i-Aqdas from every trace of their contamination. Measures under way to effect transfer of title deeds of the evacuated property to the triumphant Bahá'í community.
--Shoghi
[Cablegram, September 6, 1957]

The "purification" is described in pages 248 and 249 of The Bahá'í World: Volume 13 (1954-1963)...

In April, 1957 Shoghi Effendi announced to the Bahá'í world that an expropriation order relating to the "entire property owned by Covenant-breakers within the Haram-i-Aqdas" had been issued by the Treasury Department of the Government of Israel and published in the Israel Official Gazette. Behinds this lay a hard and protracted struggle, waged in the Guardian's name by Leroy Ioas, Hand of the Cause in Haifa and Secretary-General of the International Bahá'í Council. An appeal against the appropriation order was made by the Covenant-breakers to Israel's Supreme Court, but on June 3, 1957 Shoghi Effendi cabled the triumphant news that the order had been upheld, "enabling the civil authorities to enforce the original decision and proceed with the eviction of the wretched remnants of the once redoubtable adversaries . . ." On September 6, 1957 a further cable announced their "complete evacuation . . . and the purification . . . of the Haram-i-Aqdas from every trace of their contamination." At long last the Qiblih of the Bahá'í world had been cleansed and the way opened to fulfill, in future decades, the Guardian's vision for the construction of a "stately and befitting Mausoleum designed to enshrine the holiest Dust the earth ever received into its bosom."
It had been Shoghi Effendi's wish to direct in person the razing of the buildings evacuated by the enemies of the Cause, but this was not to be, and it fell to the Hands of the Cause in Haifa to carry out this task. It was their first endeavour, and by December, 1957 no trace of the buildings was left. They then proceeded to enlarge the gardens of the Haram-i-Aqdas according to the Guardian's plan, covering the site of the buildings entirely, and raising the third terrace he had planned toward the east, above the two he himself had completed. To the east of the Mansion a long strip of garden was planted, comprising four thousand square metres, also part of the Guardian's plan.
The Hands succeeded, moreover, in effecting the Guardian's purpose to transfer the title deeds of this evacuated property "to the triumphant Bahá'í community." In a deed of sale from the State of Israel, thirteen separate titles for the Shrine of Bahá'u'lláh , the Mansion of Bahjí, and all the newly-acquired properties were transferred to the name of the Israel Branch of the National Spiritual Assembly of the Bahá'ís of the United States.
Thus did the Sign of God on earth achieve ascendancy in his last hours, glorifying his ministry, and fulfilling one stage of his own promise for the World Centre of the Faith: "Resistlessly will this Divine institution flourish and expand, however fierce the animosity which its future enemies may evince, until the full measure of its splendour will have been disclosed before the eyes of all mankind."

It should be noted that in this text Shoghi Effendi is called "the Sign of God on earth," which is what the term "Ayatollah" means.
Also, the "thirteen separate titles" include some property that a November 12, 1952 cablegram sent by Shoghi Effendi announced as "acquisition of vitally-needed property" of the Mansion of Bahji and the area around it from "the Development Authority of the State of Israel...The exchange of said property, including land and houses, was made possible by the precipitate flight of the former Arab owners."
The "purification" would continue under the Universal House of Justice, who on November 11, 1965 sent a cable announcing the "removal from immediate precincts (of the) holy shrine (of) Bahá'u'lláh remains (of) Mirza Díyá'u'lláh."

26 Purification of the Most Holy Shrine of Bahá'u'lláh, the Qiblih of the Bahá'í World 11 NOVEMBER 1965
To all National Spiritual Assemblies
26.1 ANNOUNCE BAHA'I WORLD REMOVAL FROM IMMEDIATE PRECINCTS HOLY SHRINE BAHA'U'LLAH REMAINS MIRZA DIYA'U'LLAH YOUNGER BROTHER MIRZA MUHAMMAD ALI HIS ACCOMPLICE IN EFFORTS SUBVERT FOUNDATIONS COVENANT GOD SOON AFTER ASCENSION BAHA'U'LLAH. THIS FINAL STEP IN PROCESS PURIFICATION SACRED INTERNATIONAL ENDOWMENTS FAITH IN BAHJI FROM PAST CONTAMINATION WAS PROVIDENTIALLY UNDERTAKEN UPON REQUEST FAMILY OLD COVENANT BREAKERS A PROCESS WHOSE INITIAL STAGE WAS FULFILLED BY ABDU'L-BAHA WHICH GATHERED MOMENTUM EARLY YEARS BELOVED GUARDIAN'S MINISTRY THROUGH EVACUATION MANSION ATTAINED CLIMAX THROUGH PURIFICATION HARAM-I-AQDAS AND NOW CONSUMMATED THROUGH CLEANSING INNER SANCTUARY MOST HALLOWED SHRINE QIBLIH Bahá'í WORLD PRESAGING EVENTUAL CONSTRUCTION BEFITTING MAUSOLEUM AS ANTICIPATED BELOVED SIGN GOD ON EARTH.
UNIVERSAL HOUSE OF JUSTICE