Various systems and methods for using a directory based coherency protocol
in a system that employs a split ownership and access right cache coherence mechanism
are disclosed. A computer system may include a directory, several active devices
configured to access data, an address network configured to convey coherence requests
point-to-point between the active devices and the directory, and a data network
configured to convey data between the active devices. Each active device includes
a cache configured to store data accessed by that active device. An ownership responsibility
and an access right associated with a first coherency unit in a first cache transition
at different times.