Reuse by you or by someone else.

Viruses and spyware generally reside as programs files and the data are usually fine. therefore as long as no programs can run from that drive you will be able to work on in internally.

Quick format on your own computer will work as long as the infected drive is a secondary drive and you will be the one using it again. This will just 'delete' files which will only change the first bit of the name and make to rest of the sectors available to be written over. This quick and dirty method will be fine as long as you just start using the disk it will be fine overwriting all files over time. The upside is convenience. The other side (I don't say downside because it may not be) is that the files COULD be recovered as long those particular locations have not been overwritten.

The next level is a full format which is really not different form quick format except it also reads sector by soector and locates bad sectors, separating them out.

Wiping - as offered with CCleaner or other programs mentioned. That will will overwrite the sector making recovery almost impossible. The more times it is over written the more secure the disk.