A Closer Look II (Write)
- Px controller awaits ACKs from all those nodes
- Px controller delivers block to cache in dirty state
- Dirty bit is ON
- Home notifies owner Py of Px’s a write request
- Py controller invalidates its blk, sends data to Px
- Home clears yth presence bit, turns xth bit ON and dirty bit stays ON
- On writeback, home stores data, clears both presence and dirty bits
When shared is replaced in Px cache, notifying home
is optional -- a replacement hint -- to avoid invalidate