How to cleanly uninstall MariaDB

I've been using MariaDB on my server. It seemed to be hacked. I couldn't restart mariadb, and I deleted it with package manager yum. However, after reinstalling that I still experienced some problems (they didn't disappear).

There is an opinion http://superuser.com/a/778269/387511 that some files such as databases are not removed during MariaDB uninstall. Is it true, and what should I take care of when uninstalling MariaDB?

Thank you. I've used site search but couldn't find an answer in the official documentation. I suggest adding this to the part about installation of MariaDB.