Memory blocks are associated with each memory level of a hierarchy of memory levels. Each memory block has a matching key capability (MaKC). The MaKC of a memory block governs access to the memory block, in accordance with permissions specified by the MaKC. The MaKC of a memory block can uniquely identify the memory block across the hierarchy of memory levels, and can be globally unique across the memory blocks. An MaKC of a memory block includes a block protection key (BPK) stored with the memory block, and an execution protection key (EPK). If a provided EPK for a memory block matches the memory block's BPK upon comparison, access to the memory block is allowed according to the permissions specified by the MaKC.