As of the effective date of withdrawal of a participating governmental unit, the Board of Trustees shall transfer to the administrative board of the local pension system or new State system the portion of the assets that are allocable to the withdrawn employees as determined under § 21–305.5, § 21–305.6, § 21–306, § 21–306.1, or § 21–306.2 of this article. The administrative board of the local pension system or new State system shall hold the transferred assets in trust to provide retirement benefits for the withdrawn employees.