1. A method of migrating a virtualized computing instance between source and destination virtualized computing systems, comprising: executing a first migration workflow in the source virtualized computing system, where a host computer in the source virtualized computing system executing the virtualized computing instance is a source host in the first migration workflow and a first mobility agent in the source virtualized computing system simulates a destination host in the first migration workflow; executing a second migration workflow in the destination virtualized computing system, where a second mobility agent in the destination virtualized computing system simulates a source host in the second migration workflow and a host computer in the destination virtualized computing system is a destination host in the second migration workflow; and transferring, during execution of the first and second migration workflows, migration data including the virtualized computing instance between the first mobility agent and the second mobility agent over a network.