Synchronization of group state data when rejoining a member to a primary-backup group in a clustered computer system

An apparatus, program product and method to synchronize group state data in a primary-backup group in connection with the rejoining of a member to the primary-backup group in a clustered computer system. Each member in the group includes a copy of replicated group state data for the primary-backup group. In connection with rejoining the member, it is determined whether the rejoining member is the primary member for the primary-backup group. Then, a selection is made between member and group overwrite operations based upon such determination. The member overwrite operation includes overwriting the copy of the replicated group state data for the rejoining member with data from the copy of the replicated group state data for an existing member in the primary-backup group. The group overwrite operation includes overwriting the copy of the replicated group state data for the existing member in the primary-backup group with data from the copy of the replicated group state data for the rejoining member.