As I've been approached a few times now about the SCCM interview, here my statement and my advice on the matter for everybody to read:
Best advice I can give you is the one one I've been given by an OPM myself:
Think about all the qualities of a SCCM eg leadership, customer service, organization,... and try to remember a situation when you used those skills yourself.
All the questions they ask you are like: Tell us about a situation when...
So have lots of examples ready for everything you can think of. Make sure they are about you and not about a team achievement.
Oh, and be ready for the usual stuff like: why do you want to be a senior.
Be yourself and relax. Remember that they want you to get it right too! I was very nervous and not very confident because I applied for CRA before and didn't get it because of the interview but I prepared really hard with the advice I just gave you and it paid of.
Good luck!