To delete precomputed clips:

1. On your Avid, go to Tools -> Media Tool
2. Select all the precompute clips that have the watermark on them. Be careful NOT to select any title or key media. Normally the clips to delete will be called something like sequencename,S_EffectName. You can check which clips have the watermark by looking at the Frame or Script view.
3. Once you have selected the appropriate clips, delete them by pressing Delete.