Remove a package installed from a ppa

to list the ppa the package comes from:

apt-cache policy packagename
e.g.
apt-cache policy cairo-dock

the output is something like
http://ppa.launchpad.net/cairo-dock-team/ppa/ubuntu/ trusty/main amd64 Packages

to downgrade  it
sudo -E ppa-purge ppa:cairo-dock-team/ppa

sources:
http://askubuntu.com/questions/32835/whats-the-name-of-ppa-for-ppa-purge
http://askubuntu.com/questions/307/how-can-ppas-be-removed