Yes. You have do purging of impure income irrespective of whether you are liable to pay Zakat or not. Zakat is one of the five pillars of Islamic fundamentals. It is obligatory for a person who falls under the category of having wealth over the nisab. On the other hand, purging is purification of unintended impure income earned on account of investment activity in securities which are themselves not interest based (shares).
Allah knows best...