Home menu button

I have a WordPress Multisite subdomain installation, and I would like to make a change to Home button url (main horizontal menu, left hand side) so it is showing domain.com instead of subdomain.domain.com

I know that it ultimately leads to the same place, which is the domain.com, but when I point my mouse over the Home button, it is showing the subdomain.domain.com address on the bottom left side of the screen. I want it / need it (I have my personal reasons) to be domain.com 100% of the time.

If anybody has an idea how to change that, please let me know (I know I need to modify a template, possibly header.php).

Thank you.