Snooping To Solve Coherency
•The
cache controllers can “snoop” on the bus, meaning that they watch the events
on the
bus even if they do not issue them, noting any action relevant to cache lines they
hold
•There
are two possible actions when a location held by processor A is changed
by processor
B
•Invalidate
-- mark the local copy as invalid
•Update
-- make the same change B made
The unit of cache coherency is a cache
line or block