Exclude Subdomains

We have a site (eg. www.mydomain.com) and a test site (e.g. test.mydomain.com) where we perform major changes to Drupal before applying them to the live site. From time to time, I need to copy the data from the live site over to the test site.

After I installed mobile tools on the live site, I had to copy the database contents over to the test site to try something unrelated to this module. After I did that, whenever I tried to access the test site from a desktop browser, it redirected to the live site. I disabled the Mobile Tools module and copied the database over to our test site and I was then able to access the test site normally.

I know you can exclude pages from redirection, but can you also exclude subdomains?