A content delivery (CD) service in a CDN maintains property invalidation information on said CD service including, for each property, a list of one or more group invalidation commands. New group invalidation commands are added by selectively merging one or more invalidation commands to form a merged invalidation command and inserting the merged invalidation command into said list, wherein the merging is based on a length of common prefix of elements in said list. A per property common prefix list is maintained for invalidation commands in each property list.