Tempted to say 'left aligned', as right aligned text is generally harder to follow in non-arabic languages. Simply aligning text to a margin just because it is a margin does not make sense. The better practice is to align your text in relation to the other design elements on the page (photos, icons, background if any, graphic elements, etc).
Sometimes the actual content can lead to using a right flowing text box, but we don't know if that's the case here. It depends on your design, font sizes, is it a headline or body text, and how much text are you actually working with?
Not having seen your actual design, i could only recommend the generally 'usual', or most likely, solution: left aligned.