A globally integrated testbed for various experiments of distributed applications based on the edge cloud computing was constructed and operated as part of an international joint research program, Japan-US Network Opportunity 2 (JUNO2). The testbed consists of many virtual machines (VMs) at Kyushu Institute of Technology (Kyutech), The City College of The City University of New York (CCNY), StarBED (a large-scale PC cluster testbed), and RISE (a wide-area OpenFlow testbed) over multiple Layer-2 virtual networks (VLANs) through collaboration with international research and educational networks. Those VLANs are used as the data and the control planes with a single OpenFlow controller and twelve OpenFlow switches. As an example, this paper introduces an experiment of VM migration among CCNY, Kyutech, and StarBED for a global virtual collaborative working environment. An OpenFlow-based multicasting scheme is adopted for efficient use of the bottleneck network bandwidth in replicating a large VM environment from CCNY to two sites in Japan. The implementation details on the global testbed and the experimental results are reported, verifying that the multicast-based transfer halves the elapsed time of VM migration compared with the unicast-based transfer.