code: @Override
      synchronized final void clearPartCaches() {
          if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled())
              SibTr.entry(this, tc, "clearPartCaches");
          hdr2 = api = payload = null;
          if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled())
              SibTr.exit(this, tc, "clearPartCaches");
      }
docs: Clear the cached references to other message parts.