Sorry, i haven't explain well.
By default vmware will reserve 10% for memory compression. This is the memory of the VM. It is the last process used by your host before swapped. The memory is reserved but not used. This cache will be used when your host doesn't have any memory available.
Here a great post about memory reclaimation : Vmware vSphere 4.1 Memory Compression Understanding | GeekSilver's Blog
Regards,
Julien