[thredds] aggregation caching: cache cleared when Tomcat restarted?

Hi All,
I recently upgraded to TDS 4.2. A few of my datasets use a joinExisting NcML 
aggregation, such as:



        <aggregation dimName="time" type="joinExisting" timeUnitsChange="true">
          <scan location="/export/lawelawe1/model/tide/netcdf_data/mhi/elev/" 
suffix=".nc"/>
        </aggregation>


I've noticed that these take several minutes to load the first time I try 
accessing them in TDS (such as clicking on the OPeNDAP service) each time I 
have restarted Tomcat. Does this mean that the aggregation cache is being wiped 
when I restart Tomcat? I have set my aggregation caching in threddsConfig.xml 
as so:



  <AggregationCache>
    <scour>24 hours</scour>
    <maxAge>30 days</maxAge>
  </AggregationCache>


This led me to believe that the cache would persist for 30 days, regardless of 
restarting Tomcat. Is that an incorrect assumption or am I doing something 
wrong?
Thanks,
John Maurer
Hawaii Ocean Observing System (HiOOS)
University of Hawaii at Manoa