zsh completion after installing/removing packages

Question

How does zsh figure out currently installed packages on Debian, and how can I update that information? After running apt-get install, zsh won't autocomplete that package as a possible parameter for apt-get purge or apt-get remove. The only way I can get it to update is to run a new shell. None of the tricks I've found seem to work: rehash or even rm ~/.zcompdump && compinit don't help.

Bash recognizes package installs and removals, and modifies the possible parameter lists for apt-get remove/purge accordingly, without any user interaction. This is using the default configuration on Debian wheezy.

With the default configuration for zsh, I don't get any parameter completion for apt-get at all. I'm using the following custom rc to get completion (with the above caveat):

autoload -U compinit
compinit
eval `dircolors -b`
PS1="%n@%M:%~ > "
zstyle ':completion:*' list-colors $LS_COLORS

Answer 1

# auto rehash commands
# http://www.zsh.org/mla/users/2011/msg00531.html
zstyle ':completion:*' rehash true