Signalling Their Data
Three control lines suffice for the protocols we’ve discussed:
- Shared -- drive control line if any processor, except the requesting processor, has a copy of the block
- Modified -- drive control line if the processor has the block in modified state
- Release -- every controller drives line until it has processed request, then release means others are OK
Note complications if (clean) data can be delivered
from multiple caches ... need priority to pick one