Depends what it's made of... Cat pee is very resilient so Clorox, fantastic, Nature's miracle works quite well but not as harsh. There's another cleaner Jackson Galaxy recommends for cat urine I can't remember the name. The harsher chemical ones you'll need to make sure are dry before the box is exposed to the kitty again.
Why did your cat per in the toy box? Was it's litter box dirty?
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