Hi, Diego

Unfortunately you cannot clean the recently viewed items in RTC Web Interface(all CLM components) because the info is in the database.
If you go to RTC admin page > Advanced properties, you may set  ViewHistoryScrubTask from 30 (or  ViewHistoryScrubTask(or ViewHistoryService in later version) to 1(0) which will only show you 1 recently viewed.
(you may need to wait for 1 hour to see the scrub task working).

There is an existing enhancement request to allow the user to Clear All:
https://jazz.net/jazz/web/projects/Rational%20Team%20Concert#action=com.ibm.team.workitem.viewWorkItem&id=51133

You may want to add your comments in the above work item.

Thanks