time to try a little exploratory testing.
We see this willingness to work outside expertise in agile teams when people collaborate to swarm around a feature. People are willing to work outside their expertise but not far from it. To learn more about this ability, ask, "Tell me about a time you took on work to help the team. What was that like?"
A candidate may not be able to answer that question. You may then have to set the context with something like, "We work on things we may not be comfortable with in order to finish a feature for an iteration. Have you ever been in that position?" If the candidate does not say yes, you'll have to ask the question differently. For example, I've had some success with the following: "Tell me about a time you did something you thought was not in your job description. What did you do?"
These may not be the only behaviors you need for your agile team. Make sure you do a job analysis to see how your agile team is different, and then you'll know the kinds of candidates to consider.