You can clear your Recently Viewed page using the "Clear all" link.
That will remove some things, but not all; the last four items you viewed are also shown on your Summary page, and some searches and items may appear on your main eBay page. Those can be displaced by performing additional searches and viewing additional items.
If you do not want others to see items you have viewed, do not share your eBay account with anyone, and be sure to sign out and clear your browser history after using eBay.
