A system and method for determining registration to a packet-switching (PS) domain or a circuit-switching (CS) domain via a single request is discussed herein. A single request includes a query hierarchy to query a node of a first domain and then, if the UE is not registered with the first domain, to query a node of a second domain. The request includes an attribute value pair (AVP) to determine which domain to query first and which node of the first domain to query. The domains of the AVP are acquired from a list to permit multiple domains to be queried with the single request.