A method for concurrent garbage collection and mutator execution in a computer system includes scanning a first cache line for a non-local bit. The non-local bit is associated with a root object. A done bit associated with the first cache line is set. A second cache line to find a first object that is referenced by the root object is located. A mark bit and the done bit associated with the second cache line are set. The first and second cache lines are scanned for unset done bits. If an unset done bit is detected in either the first or the second cache line, then the cache line associated with the unset done bit is rescanned to determine whether there are any modified object references.