An event tracking hardware engine having N (≧2) caches is invoked when an event of interest occurs, using a corresponding key. The event tracking engine stores a cumulative number of occurrences for each one of the different kinds of events, and searches in the N caches for an entry for the key. When an entry for the key is found, the engine increments the number of occurrences if no overflow of the cumulative number of occurrences would occur. However, if the incrementing would cause overflow, then instead of incrementing the cumulative number of occurrences, the engine promotes the entry for the event of interest to a next higher cache.