That can be identified as a finalization-driven sweep. The object whose refcount hits zero is finalized, and the routine for that drops its references to other objects.
Garbage collection also traces dead objects. Or at least some kinds of GC implementations that are not copying. when the marking is done, the heaps are traversed again to identify dead objects, which are put onto a free list. That's a trace of dead objects. (Under copying collection, that is implicit; live objects are moved to a new heap and the vacated space is entirely made available for bump allocation.)
Garbage collection also traces dead objects. Or at least some kinds of GC implementations that are not copying. when the marking is done, the heaps are traversed again to identify dead objects, which are put onto a free list. That's a trace of dead objects. (Under copying collection, that is implicit; live objects are moved to a new heap and the vacated space is entirely made available for bump allocation.)