A method of operating a distributed computer system using a serialising token as a supplement to locks for accessing the same page by different processes and ensuring coherence between data caches and a shared access backing store supporting the processes defined onto multiple processors. A shared lock and a new token are issued by a local lock manager (LLM) and local cache manager (LCM) in response to a page read request from a process. An exclusive lock, an invalidation of all cache resident copies of the page, a cache write through to backing store of the changed page, a copyback of a new token, and lock release are responsive to a page write/update request from a process where the token issued to the process during a prior request matches the token stored with a cache resident copy of the page. Otherwise, a write request fails and the process must first issue a read request to the page of interest.