Merge protocol for clustered computer system

An apparatus, program product and method utilize ordered messages in a clustered computer system to defer the execution of a merge protocol in a cluster group until all pending protocols in each partition of a group are handled, typically by ensuring either cancellation or completion of each pending protocol prior to execution of the merge protocol. From the perspective of each group member, the execution of the merge protocol is deferred by inhibiting processing of the merge request by such member until after processing of all earlier-received pending requests has been completed.