Any text editor can be used to scrub the text as long as it supports the TXT format. TXT files don't have any "hidden" formatting in them so what you see should be what you get.
However, when you scrub the text you won't be able to keep any formatting at all. You will need to re-apply it in Scribus, preferably using styles.
It's worth noting that word Processors - like OO/LO/Word/etc. - usually "cheat" when using bold and italic. They basically take the vectors that make up a character and manipulate them to create what they call bold or italic. For instance, for "italic" they usually skew the vectors at an angle, and for "bold" they will increase the width between the "outside" and "inside" of the glyph. This is an over-simplification but it gets the idea across.
Scribus, on the other hand, uses fonts properly and only allows you to use bold or italic if you have a bold or italic variant of the font available. This means that it's difficult to translate the use of, for example, "bold" in a word processed document to Scribus.
For instance, say you format some text in LO to be bold, then you import the text into Scribus. Scribus would have to look and see whether you really do have a bold variant of each font that is formatted in bold and convert it. This might sound simple but some fonts have variants for bold that aren't called "bold", such as "heavy" or "black". It's a lot of hassle and you can't be certain that the result would be what you wanted as the "bold" that the word processor applied would look different to how a real bold font would look. The formatting would look different.
And the same thing goes for italic, and then there's bold and italic together which adds to the problem.
The image attached may be useful. The text at the top is from Scribus and the text at the bottom is from LO. The differences can be difficult to spot but look at the "o" in "bold". The shape of the letter is slightly different (look at the top and bottom of the counter, or "hole", inside the letter). The problem is more evident in the "t" of "italic", where you can see that LO has mangled the letter's ascender during its manipulation.
All in all, if you apply all of your formatting in Scribus you can be sure it's going to be correct, typographically.
If you need to keep track of where to apply formatting in a text file then using some simple "control sequences" of your own can be useful. For instance, the text could look like this: "This is some {b}bold text and some {i}italic text." You can then search for the "control sequences" once the text has been imported into Scribus and apply the relevant styles as appropriate. It's not perfect by any means but it helps as a reminder. Maybe someone else reading this has a better way of doing it.
I hope some of this has helped.