I subscribe to www.dummiesdaily.com which sends me tips and info about a few topics, one is cats, one is dogs. The following came from an email tip I got today:
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TODAY'S eTIP(TM): Scratch Out Your Territory

Like urine spraying, scratching is a form of territory marking. The bottoms of a cat's feet are filled not only with tiny capillaries that dilate and perspire (which helps the cat regulate his body temperature), but also with scent glands. When a cat scratches, he leaves a physical reminder to other cats and a scent marker that clearly states this is his area. Often, a cat will touch you with his paws, letting you know that you are his human.

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I wonder if this applies in multi-cat households?