Write Operation
Local Cluster: Want to do a write to location - must issued a ‘read-exclusive’ ; will cause invalidation of other shared copies. Allocate cache entry, send Read-Ex request to home cluster
Home Cluster: Directory entry in shared state; send invalidation requests to to all shared clusters; send invalidation counter and Read-Ex reply to local cluster. Directory state updated to dirty.
Remote Cluster(s): Invalidate shared copy; send Invalidate Acknowledge to the Local Cluster.
Local Cluster: Receive counter and Read-Ex reply from Home cluster. Allow CPU write to finish/
Local Cluster: As invalidation acknowledgements come back, decrement the counter. When counter reaches zero, can deallocate the cache entry
- Allows write to finish BEFORE counter reaches zero,
- Will BLOCK further shared accesses to this location until after the counter reaches zero