Abstract: A data processing system dynamically balances allocation of storage areas in a shared coupling facility that is devoted to storage of directory entries and data blocks. Each directory entry includes information regarding the validity of a data block that is locally stored by one or more processor modules in the data processing system. The system includes a coupling facility having a cache memory wherein a first portion is allocated to storage of data blocks and a second portion is allocated to storage of directory entries. Each directory entry, associated with a data block, indicates the validity or invalidity of data contained in a copy of the data block maintained by a connected computer module in its local memory. Each computer module, upon requiring a first data block and determining that (i) the first data block is present in its local memory (i.e., a buffer "hit"), but (ii) is not marked valid and (iii) is not present in the coupling facility (i.e.