Remove all subdomains sites from search result (site:mysite.com)

Hi,
i notice some strange thing when i go to google and type site:mysite.com
some of my clients blogs appears as subdomain in the search result but all the others not.
for example
client1.mysite.com
client2.mysite.com
client3.mysite.com
i use wordpress multisite and domain mapping. all the blogs are mapped.
the question is how can remove safe all the sub domains from my main multisite in the search results without make damage to mapped domain(seo) and my main site (seo).
i want only to see all my pages/posts on the main site without any clients sites.
i think i can be done easily at robots.txt but i dont want that google bot will block also the mapped domain.

Thanks