code: protected void updateLastScanFile() {
          final String methodName = "updateLastScanFile()";
          final File f = new File(lastScanFileName);
          final CacheOnDisk cod = this;
          traceDebug(methodName, "cacheName=" + this.cacheName);
          AccessController.doPrivileged(new PrivilegedAction() {
              @Override
              public Object run() {
                  FileOutputStream fos = null;
                  ObjectOutputStream oos = null;
                  try {
                      fos = new FileOutputStream(f);
                      oos = new ObjectOutputStream(fos);
                      oos.writeLong(System.currentTimeMillis());
                  } catch (Throwable t) {
                      com.ibm.ws.ffdc.FFDCFilter.processException(t, "com.ibm.ws.cache.CacheOnDisk.updateLastScanFile", "650", cod);
                      traceDebug(methodName, "cacheName=" + cod.cacheName + "\nException: " + ExceptionUtility.getStackTrace(t));
                  } finally {
                      try {
                          if (oos != null) {
                              oos.close();
                          }
                          if (fos != null) {
                              fos.close();
                          }
                      } catch (Throwable t) {
                          com.ibm.ws.ffdc.FFDCFilter.processException(t, "com.ibm.ws.cache.CacheOnDisk.updateLastScanFile", "661", cod);
                          traceDebug(methodName, "cacheName=" + cod.cacheName + "\nException: " + ExceptionUtility.getStackTrace(t));
                      }
                  }
                  return null;
              }
          });
      }
docs: Call this method to update the timestamp of the last scan in Last Scan file.