I have multiple domains listening on same ports and sharing same document root. This is a limitation of my hosting provider that lets me have multiple domains for my GSuite mail routing without using one of my limited number of add-on domains.
The problem is I see Google is indexing content for one of these domains so the URL in some Google results is not the domain I want it to be.
What options do I have to control this? The noindex directive in HTML tag meta is not an option, because document root is shared. Apparently Google advise against using robots.txt where the intended purpose is to hide from Google results. And I also do not have shell access to modify the HTTP header responses.
Edit: I should say I've deleted the DNS A record. While that prevents browsing to my website via that domain, I'm not sure if that'll eventually help the Google situation.