Regarding to cache primitive definition.

How about to deduct to have the following cache primitives;

 - Invalidate
        Discard cache contents which belongs to target address
        range from cache, if any.

 - Synchronize
        Make sure target address range contents synchronized
        with cache, if any.

 - Flush
        Make sure target address range contents synchronized
        with cache, if any, then discard the copy in cache.

For write-thru cache, Synchronize op would be noop since the target
address range contents is always synchronized by definition, while
Flush op would be a synonym of the Invalidate op.  For write-back
cache, 3 primitives do the differents, so-so.

Tohru Nishimura
Nara Institute of Science and Technology