1. A method for identifying roots for a garbage-collection operation in a computer system that supports an object-addressed memory hierarchy, comprising: looking up an object table entry that corresponds to an object in an object cache, wherein the object table entry contains an evicted bit, which is set when any part of the corresponding object is evicted from the object cache, and a corresponding physical address in main memory for the object, and wherein the object table entry is located within an object table object that is part of a hierarchical object table; determining that the evicted bit is set for the object; and examining the object to determine if the object contains references to a target area in an object heap that is being garbage collected, and if so, using the references as roots for a subsequent garbage-collection operation of the target area.