It has very simple solution. You need to put the Robots.txt file in the root folder of your sudomain (i.e xyz.example.com).
After that you can use Robots meta tag to disallow SE from crawling your site (i.e xyz.example.com/abe, xyz.example.com/abcds).
This is definitely the case when you should use meta tag "robots" and "noindex" the subdomain or what ever pages you want to hide from serps.
After that, you could consider using url removal tool from google and getting rid of pages you don't want to see in serps, which will speed up the process a bit.
Do not go with robots.txt and blocking content of this ...