Washing hands between Mincha and Maariv:
If one washed his hands prior to Mincha he is not required to rewash his hands prior to Maariv, so long as he did not remove his mind from his hands in the interim period.
If one left the Shul and returned: If one did not consciously guard his hands then he is to rewash prior to Maariv. If however one made sure to guard his hands in the interim then he is not required to wash his hands a second time.
 M”B 333/16