A system for increasing the efficiency of migrating, at least in part, a virtual machine from a source host to a destination host is described wherein the content of one or more portions of the address space of the virtual machine are each uniquely associated at the source host with a signature that may collide, absent disambiguation, with different content at the destination host. Code in both the source and destination hosts disambiguates the signature(s) so that each disambiguated signature may be uniquely associated with content at the destination host, and so that collisions with different content are avoided at the destination host. Logic is configured to determine whether the content uniquely associated with a disambiguated signature at the destination host is already present in the destination host memory, and, if so, to back one or more portions of the address space of the virtual machine having this content with one or more portions of the destination host memory already holding this content.