1. A system for cache external writing, having a system interconnect for communication among multiple devices coupled to the system interconnect, the devices operative to modify storage locations, comprising: a system memory coupled to the system interconnect; a cache memory coupled to the system interconnect, the cache memory having a unique identifier and operative to contain data corresponding to locations in the system memory; write enable logic coupled to the system interconnect, the write enable logic operative to detect a communication signal according to the unique identifier; and a communication signal generated by one of the multiple devices connected to the system interconnect and received by the write enable logic, the communication signal operative to communicate to the cache memory when writes to the system memory should be written to the cache memory.