You can use Drush and the Acquia Purge module to completely clear varnish and the Acquia CDN for a site. This can be done from the command line or in a script.
drush p:invalidate everything --uri=example.com
The above command will clear all external caches for the example.com site.
If you have multiple domains for one site, it will clear all of the domains under that site.
You host several site with the domain names of blue.com and red.com:
The following command is run:
drush p:invalidate everything --uri=blue.com
The above command will clear all caches for: blue.com, foo.blue.com, bar.blue.com, and bluespecialoffer.com
But the domains under the Second site will not be touched. Run the same command above, replacing "blue.com" for "red.com".