How to reset Drupal's content cache / deleted content?
Unless you are using some module that I havent heard of (certainly possible) to give autocomplete style info as you are entering a node title, then I think the functionality you are describing is actually something being done by your browser. 

You can alter your form to add automcomplete="off" to your title field (see https://stackoverflow.com/questions/2530/how-do-you-disable-browser-autocomplete-on-web-form-field-input-tag)