remove i386 from amd64 Ubuntu systems

Upgrading an amd64 Ubuntu to oneiric caused the package manager to load not only amd64 list of packages, but also i386 ones. The solution is to remove the multiarch file from /etc/dpkg/dpkg.cfg.d :
# cd /etc/dpkg/dpkg.cfg.d 
# mv multiarch multiarch.backup 
# aptitude update 
Since Ubuntu 12.10, you should use %dpkg --remove-architecture i386