WebRequest.ClearCookie
From Xojo Documentation
Method
WebRequest.ClearCookie(Name As String, Domain As String = ".", Path As String = "/")
New in 2011r2
Supported for all project types and targets.
New in 2011r2
Supported for all project types and targets.
Removes the Name cookie set by a previous request. The Domain and Path must exactly match the values that were used to create the cookie.