[20] A directory controller can send invalidates for lines that have been replaced by the local cache controller. To avoid such messages, and to keep the directory consistent, replacement hints are...

[20] A directory controller can send invalidates for lines that have been replaced by the local cache controller. To avoid such messages, and to keep the directory consistent, replacement hints are used. Such messages tell the controller that a block has been replaced. Modify the directory coherence protocol of Section 5.4 to use such replacement hints.