Dunno about moving house, but salt is powerful magic. Spirits can't cross it. It used to be traditional in many parts of the the UK for a dish of salt to be placed upon a dead body to prevent any 'problems', or for salt to be sprinkled around the corpse, for the same reason. I seem to remember that salt crops up in the tale of Tamerlane with just this function.

And yes, one way to protect your house is supposed to be to open your doors, order the spirits out (they must obey, apparently), and then sprinkle salt across the thresholds to stop the buggers sneaking back in!

However this doesn't seem to bear any relation to the rhyme your co-horse?! ;) half remembers.