When you are shifting to another domain within the same company it's easy to showcase your skills as the company is aware of rapport and your past work in detail. But when finding a new job in a different domain they need to know more and for that you need to show the relevant projects that you have done in the new domain. The key element is which ever new domain you pick, you make sure you have projects done in that and have it ready to show for example if it's in Design give the link to your Behance profile. The answer has to come from your core motivation to pick the new domain as either the next step in your career or your calling in that domain because of your interest in that field. And add to how your past work and made you ready for the new domain if you can make that link.