Multicasting is a challenging task that facilitates group communication among the nodes using the most efficient strategy to deliver the messages over each link of the network. In spite of significant research achievements in recent years, efficient and extendable multicast routing in Mobile Ad Hoc Networks (MANETs) is still a difficult issue. To enhance performance and to enable scalability we have proposed a domain-based Extendable Multicast Routing Protocol (EMRP) for hierarchical multicasting in MANET environments. In the proposed technique, each domain has a sub-source that reduces the path length between the original source and intended receiver which solute the scalability issue. We have analyzed the performance with respect to a variety of parameters for different mobility speed and group sizes. Results obtained through simulations demonstrate enhanced performance in packet delivery ratio and end-to-end delay of the proposed technique as compared to the existing ones.