Cache memory and method for handling effects of external snoops colliding with in-flight operations internally to the cache

Abstract

A cache memory that completes an in-flight operation with another cache that collides with a snoop operation, rather than canceling the in-flight operation. Operations to the cache comprise a query pass and one or more finish passes. When the cache detects a snoop query intervening between the query pass and a finish pass of the in-flight operation, the cache generates a more up-to-date status for the snoop query that takes into account the tag status to which the in-flight finish pass will update the implicated cache line. This is necessary because otherwise the snoop query might not see the affect of the in-flight finish pass status update. This allows the in-flight finish pass to complete instead of being cancelled and the snoop finish pass to correctly update the status after the in-flight finish pass, and to provide modified data from the cache line to the externally snooped transaction.