A method for maintaining data coherency in a shared-memory computer system having a plurality of nodes divides the local memory of a given node into one or more blocks and stores a data record for each block indicating a plurality of node groups and a selection of the node groups. Each selected node group represents a number of nodes, and selected node groups represent at least one node that has requested access to the block. In response to receiving an access request from a requesting node that may or may not be in a selected node group, the method and system update the data record to indicate the correct selection. If the requesting node is not in any node group, the data record is adjusted to have new node groups, one of which represents the requesting node.