Before clearing your browser cache be sure to log out of Blackboard and any other sites and then close and restart your browser after clearing the cache. Then, instructions depend on the particular browser:
On both Mac and PC look under tools and select "Clears Recent History"
How can I copy material from one coursesite to another?
It's a new term, and you want to use material from your old Blackboard coursesite in this term's new site. You can copy material, but you'll need to be "instructor" or "teaching assistant" in both sites.