debian - how to reinstall a package

I always thought that apt-get install --reinstall would reinstall a package, but it doesn't seem to work. I broke a file that belongs to a package (/etc/xen/scripts/vscsi) and want it reinstalled from the package source but it doesn't work - even if I delete the file, --reinstall doesn't put it back again. The man page doesn't tell me anything immediately obvious, although the solution will probably come to me as soon as I've hit send here. Any suggestions? Thanks James