typedef enum _MEMORY_CACHING_TYPE
{
         MmNonCached = 0,
         MmCached = 1,
         MmWriteCombined = 2,
         MmHardwareCoherentCached = 3,
         MmNonCachedUnordered = 4,
         MmUSWCCached = 5,
         MmMaximumCacheType = 6
} MEMORY_CACHING_TYPE;

Windows Vista Kernel Structures