Data access routing circuitry 4, 6 is provided for routing data access request to a selected destination node. The data access routing circuitry supports read requests requiring a read response, write requests requiring a write response and at least one type of atomic data access request requiring both a read response and a write response. Resource allocation circuitry 70, 71 is provided to control allocation of resource for handling data access requests which require a read response. The resource allocation circuitry 70, 71 reserves resource for handling the at least one type of atomic data access request and prevents use of the reserved resource 76 for handling read requests.