WordPress MU

I'm a bit confused about how I go about making a plugin no longer available across wpmu. I've used the "globally deactivate" option on the admin plugins menu, but that doesn't seem to be doing anything. . .I see a page stating that the plugin is being deactivated on every blog, but when I go into individual blogs that were using it, I can still see it both available in the plugin list and active.

Am I missing something obvious?

Not too sure about the global deactivation thing but if it is important that you remove the plugin form all the blogs you can simply delete the plugin from your plugins directory and it will no longer show up in the available plugins list.

I would obviously keep a copy of it in case something goes wrong or if u want to put it back on at a later date.