A server logical partition (LPAR) of a virtualized computer includes shared memory regions (SMRs). The SMRs include pages of the server LPAR memory to share with client LPARs. A hypervisor utilizes an export vector to associate logical pages of the server LPAR with SMRs. The hypervisor further utilizes a reference array to associate SMRs with client LPARs that have mapped at least one physical memory page of the SMR from a logical page of the client LPAR memory. In processing an operation to unmap one or more shared physical pages from one or more LPARs, the hypervisor uses the export vector and reference array to determine which LPARs have had a mapping to the physical pages.