6.18 System Interface Coherency
To prevent a SYNC instruction from graduating, the external agent must negate the SysGblPerf* signal no later than the same SysClk cycle in which it issued the external completion response for a processor read or upgrade request which is not yet globally performed. Also, the external agent must negate the SysGblPerf* signal no later than two SysClk cycles after the address cycle of a processor double/single/partial-word write request which has not yet been globally performed.
The SysGblPerf* signal may be permanently asserted in systems implementing a sequential consistency memory model.