Described herein is a cache coherency protocol having five states: Modified,
Exclusive, Shared, Invalid and Forward (MESIF). The MESIF cache coherency protocol
includes a Forward (F) state that designates a single copy of data from which further
copies can be made. A cache line in the F state is used to respond to request for
a copy of the cache line. In one embodiment, the newly created copy is placed in
the F state and the cache line previously in the F state is put in the Shared (S)
state, or the Invalid (I) state. Thus, if the cache line is shared, one shared
copy is in the F state and the remaining copies of the cache line are in the S state.
