Our monitoring system and Web Switch currently check Matrix with a request similar to:
GET / HTTP/1.1
Accept: /
User-Agent: AppSwitch/10.0
Host: www.ourdomain.com:80
expect _designs
This probably usually hits squid (in front of Apache) and when it does hit Apache it probably creates a new session. I'll probably add a cookie string and /_nocache to request.
What are you using?