Cache inconsistent when site has multiple domain names

I was seeing problems where old content was still being presented to anonymous users long after it should have been expired in a cron run. After much head-scratching, I think I've figured out the issue.

The site supports multiple domain names all pointing to the same Drupal site - i.e.: "example.org", "example.com", and "example.net" all point to the same site in /sites/example.org/. Each domain name was building a separate cache directory. However, because the domains all pointed to a single site, I was only running the cron job on one of the domains. An unfortunate side effect of that is that the cache was then not being expired on the other domains.

I see a few potential workarounds:

1. Run cron jobs against every domain served by that instance. Less than ideal, wastes resources, but seems to be effective.
2. Symlink "cache/example.com" and "cache/example.net" to "cache/example.org". Works fine, but requires shell access to the server.
3. Use settings.php $base_url to redirect all traffic from "example.com" and "example.net" to "example.org"

Ideally, however, it would be nice if Boost were aware of the fact that the site has multiple domains and handle it gracefully.