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Not sure if the Turbo has it, but some phones have a CLOSE ALL button on the MultiTask window (the list of apps/pages you're seeing). Other than that, unless you have an app that clears all active applications and maybe a reboot (not all phones support clearing the list upon rebooting) you'd have to swipe them away one by one.
There's no close all option in the recent apps menu on the turbo. That's usually a thing put in by the manufacturer, such as Samsung. There may be an app, but I just swipe them away. Now, if it's being cluttered by web pages, you can turn that off as an option within chrome.