Apache2 redirect domain to internal page
I have two domains pointing to a site hosted by apache2 (a.com and b.com for example). The primary domain is a.com and the website can be accessed from this domain.
However, the page a.com/test/ should redirect to b.com (not b.com/test/) to display the content from the server (as it normally would for a.com/test/) and this content should also be displayed if b.com is accessed directly.
I thought that reverse proxies might be the way to go but haven't had any luck, I was wondering if this is possible to do within my .htaccess file (both domains are pointing to the server).