So we used Google Analytics on many of our projects - but no longer do.
Still most of our visitors have those lifetime cookies __utma and __utmz set and send those to our servers with every request.
Important: the last 2 lines have the commands to clear those cookies. Replace yourdomain.com with your own domain and test if this works.
If you don’t know if the cookie is set to your main domain or your subdomain examine the cookies and find the correct path and domain like in this example:
You could use this script also to get rid of any other lifetime cookies you no longer want / need on your domain.
Oh in case you need the minified version of the above script. Here it is:
If you've read this far you might as well follow me on Twitter here.