...Dim domainName As String = "mysite.com"
Dim urlPath As String = "http://www.mysite.com/foo"
Dim regexPattern As String = String.Format("^https?://(.*?)?\.?{0}/(.*?)?/?$", domainName.Replace(".", "\."))
Dim reMatch As Match = Regex.Match(URL, regexPattern)
Response.write(reMatch.Groups(2))...