1. A method for managing memory of a runtime environment executing in a virtual machine, the method comprising: receiving cache data from an application executing in the runtime environment and storing the received cache data in one or more objects within heap memory of the runtime environment; determining, by operation of a memory management agent, a first target size for memory to be reserved within heap memory of the runtime environment; identifying at least one of the objects stored in the heap memory that store cache data for the application; replacing at least some portion of the cache data stored in the identified object with a first value; and notifying a hypervisor that at least one machine physical memory page associated with the identified object and having the first value, can be re-claimed.