Generate list of all installed packages

dpkg --get-selections > installed.txt

Deinstall all i386 packages

grep ':i386' < installed.txt.old |cut -d: -f1 | cut -f1 | xargs -n1 apt-get remove

Remove i386 architecture from DPKG Database

dpkg --remove-architecture i386

Download all needed packages and check for install candidates

apt-get -f -o Dpkg::Options::="--force-overwrite" install --reinstall $(cut -f1 < installed.txt |grep -v ':i386')

Reinstall all but i386 packages

grep -v ':i386' < installed.txt.old | cut -d: -f1 | cut -f1 | xargs -n1 apt-get -f -o Dpkg::Options::="--force-overwrite" install --reinstall

Alternatively you can reinstall all packages if no i386 packages are installed. This is good for those that are just wanting to get the box back in shape after disaster has struck.

cut -d: -f1 < installed.txt | cut -f1 | xargs -n1 apt-get -f -o Dpkg::Options::="--force-overwrite" install --reinstall