I've just flagged this question for cross-posting (to/from an external site, not within the SE-framework), and indicated in a comment that I'd done so.
I got a comment back, that there was nothing wrong with that - and looking at the referenced questions coming up as I type this, I can see that the line is not exactly clear. Examples here and here for two opposite stances on this.
So my question is: What is right? In the question I originally flagged, it is easy to google all three questions the user has currently asked and find it on other sites.
Personally, I would prefer to know that a question has also been asked elsewhere, but I would like to know the current perception on this.