There is no process for disinviting subscribers. Here's a quote from the artcle I linked to previously above.
So what happens if you start out with a public site and later decide to make it private?
First of all your site’s feeds will no longer be available. Anyone who has subscribed by RSS feed will not receive notice of new posts ... Subscribers, both WordPress.com users and those who have subscribed by email, will still show up on your Subscribers stats page. However, in spite of any misleading dashboard messages, like the one below that appears after you publish a new post, new posts are not sent out to your previous subscriber list. The only people who will be able to subscribe to your private site are the people you’ve invited to view it. http://wpcommaven.wordpress.com/2011/09/05/blog-privacy-and-subscribers/