I found this article which mentions the registry key where the URL's are kept.
To remove the cached Internet address entries, clear the History folder. To do
so, use the appropriate method:
Internet Explorer 4.0, 4.01, 5, 5.5
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1. In Internet Explorer, click Internet Options on the View (or Tools) menu.
2. On the General tab, click Clear History.
3. Click Yes, and then click OK.
If the cached addresses are still listed in the Address box in Internet Explorer,
use the following steps:
1. Quit Internet Explorer.
2. Delete all of the values except for the (Default) value from the following
registry key:
HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\TypedURLs
NOTE: Values in this registry key are listed as Url1, Url2, Url3, and so on. If
you delete only some values and the remaining values are not in consecutive
numerical order, only some of the remaining entries are listed in the Address
box. To prevent this behavior from occurring, rename the remaining values so
that they are in consecutive numerical order.