If a member of a State or local retirement or pension system transfers to another State or local retirement or pension system because of an involuntary transfer of the member’s unit to another employer, all the employer contributions on behalf of the member and interest on those contributions shall be transferred to the new system. The amount to be transferred to the new system under subsection (a) of this section shall be determined by actuarial valuation. The cost of the valuation shall be shared equally by the previous system and the new system.