Depending on the OS I would just delete it, reboot and let the OS recreate it. If you have two disks/partitions just create a new one on the 2nd partition, reboot, recreate one on the first disk and reboot again.
There's a swapfile defragmenter, but I doubt it will help with a corrupt one, just delete it like Dial suggested, and create a new one. I have a small 10GB 7200 RPM drive that I keep my swapfile on, only thing on that drive.
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