A method and apparatus to reduce unnecessary write backs of cached data to a main memory and to optimize the usage of a cache memory tag directory. In one embodiment of the invention, the power consumption of a processor can be saved by eliminating write backs of cache memory lines that has information that has reached its end-of-life. In one embodiment of the invention, when a processing unit is required to clear one or more cache memory lines, it uses a write-zero command to clear the one or more cache memory lines. The processing unit does not perform a write operation to move or pass data values of zero to the one or more cache memory lines. By doing so, it reduces the power consumption of the processing unit.