@Dave - you're correct that the usage is possessive, but incorrect in your spelling of the possessive pronoun "its." The word "it" is a pronoun, just like she or him. Similarly, the word "its'" is a possessive pronoun already, like hers or his. Just as you don't write "the car is her's," or "that's hi's hat," you don't put an apostrophe in the possessive pronoun "its."