removing iMessages completely from MacBook Pro

I have a work MacBook and somehow hooked my iMessages to it. I have checked and I am NOT signed in with my apple ID - in fact I am signed in with our work Apple ID. I have also disabled the iMessages with my Apple ID in the actual message settings. It is no longer being received on the laptop but you can still see all my personal messages. How I can I completely remove myself everywhere off this work laptop before I turn it over to someone else?

Thanks.