How do I tell default page vs page

I'm trying to create a check to distinguish between someone requesting the default page vs. explicitly requesting the default page. I'm running CF11 under IIS. My site has a default document of index.cfm. I need to determine if the user requested http://my.domain.com/ vs. http://my.domain.com/index.cfm

I cannot find any difference in the CGI scope between the two calls and I've also looked at the contents of getHttpRequestData() to no avail.