Try the command clear ip mroute * If that doesn’t work you probably will need to reboot. Let us know if you have any additional questions.
The logs on my N4032F (6.5.4.18) are filling up with the following and I'm not sure how serious they are, nor how to resolve: <189>  General[pimsmMapTask]: l7handle.c(180) 20978 %% NOTEHANDLE LIST : handle list allocation exceeded<189> PIMSM[pimsmMapTask]: pimsmsgrpttree.c(237) 20977 %% NOTE PIMSM (S,G,RPt) table max limit 1024 reached and cannot accomodate any further routes. PIMSM multicast route table (S,G,RPt) has reached maximum capacity and cannnot accommodate new registrations anymore.  
N4000 log - handle list / PIMSM Table