Typically the site admin will create some default content on My Page using shared scope. There is an old video tutorial here that explains about user scope and shared scope:
So typically My Page is setup in advance with default content and the user is allowed to re-arrange it and add/remove content and personal pages.
I'm not sure if thats what you mean about "has MyPage setup" and when you say "detect" it raises the question "detect from where?"
Hope it helps,