Reliable multicast is realized in a scalable way by tree based approaches, where the receivers are organized in an ACK tree. Usually, expanding ring search (ERS) is used to create such ACK trees. However, ERS has some shortcomings like poor scalability, strong dependency on the multicast routing protocol and the need for bidirectional multicast capable networks, which makes it difficult to use ERS as the Internet standard mechanism. In this paper we propose the Token Repository Service (TRS), which is based on a token repository and a modification of ERS. The TRS stores tokens, which represents the right for a joining node to connect to a certain parent node in the ACK tree. Performance evaluations show that the TRS approach has several advantageous compared to ERS, like improved scalability and independence of the routing protocol.