You can use .stop() as you do, but add an argument to it to also clear the queue, and then reset the top and left positions with .css() :
$('.block').stop(true).css({top: 0, left: 0});
.finish() also in the same category, but this puts all animations in their final state, which you do not want to do here. You just want to stop / clear the current animation (including any queues), and then reset the CSS properties back to their original state.
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