A user might have their browsers set to clear cookies on close, but not other saved data.. in this way most sessions are closed. This works around that case.
If a user clears all app data for a site/domain then it will be cleared. If you want to work around this, you could utilize resources/assets from other domains in conjunction but it will be more complicated. I find that most of such cases are abused for unscrupulous tracking.
If a user clears all app data for a site/domain then it will be cleared. If you want to work around this, you could utilize resources/assets from other domains in conjunction but it will be more complicated. I find that most of such cases are abused for unscrupulous tracking.