Tree-based reliable multicast protocols provide scalability by distributing error-recovery tasks among several repair nodes. These repair nodes integrate the status information of their receiver nodes and perform local error recovery for these nodes using the data stored in their buffers. In order to provide scalability and reliability, these buffers should be managed in an efficient manner. We propose a heuristic buffer management scheme that uses both positive and negative acknowledgments to achieve this goal. Under our scheme, receiver nodes send negative acknowledgments to their repair nodes to request packet retransmissions while some representative nodes send positive acknowledgments to indicate which packets can be discarded from the repair node's buffer. Our scheme provides scalability, because it significantly reduces the number of feedbacks sent by the receiver nodes, in addition, it provides fast recovery of transmission errors, since the packets requested from the receiver nodes are almost always available in their buffers.