Over the year, researchers have proposed the Core Based Tree (CBT) and Protocol Independent Multicast (PIM) protocols to route multicast data on Internet. Such protocols need to locate the Core of a group to have efficient multicast routing. In this paper, we propose a scalable distributed protocol that can be used to move the Core to near-optimal location for dynamic multicast tree, and allow the Core to migrate efficiently when the multicast tree is expanded or shrunken. In our protocol, it does not require knowledge of the complete network topology, and information of overall members is distributed among local Agents; the Core only maintains information of Agents of the group. Also, only the Agents participate in Core selection. Therefore, the proposed protocol reduces the runtime overhead and message complexity while doing Core migration.