We argue that the limit of the propagation of the heap effects of a source code modification is determined by the aliasing structure of method parameters in a trace of the method calls that cross a boundary which partitions the heap. Further, that this aliasing structure is sufficient to uniquely determine the state of the part of the heap which has not been affected. And we give a definition of what it means for a part of the heap to be unaffected by a source code modification. This can be used to determine the correctness of a refactoring.